o PnR Target: The target set in the PnR tool (e.g., via SDC set_max_transition command) is usually a fraction of the library limit, often around 70-80% of Lib_Max_Trans.
o
Provides design margin. Gives the PnR tool more
headroom to work with. Helps improve correlation between PnR timing estimates
and signoff STA results, which use more accurate extraction and timing models. Tighter
transition control generally improves noise immunity.
o Decision
Process: The exact percentage or value is often project-specific or
methodology-defined, based on:
o Technology
node characteristics.
o Foundry
recommendations.
o Past
project experience and correlation data.
o Design
goals (performance vs. power vs. area).
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